Tony Blair is to woo evangelical Christians ahead of the general election as rival faith groups play an increasingly significant part in campaigning strategy.

The prime minister will address 200 members of the Christian Faithworks group next week in a lecture on how the church can create "a more trusting society".

The move towards targeting individual faiths as part of the run-up to the likely May polling day comes after Michael Howard, the Conservative leader, made abortion an election issue for the first time in British politics at the weekend, when he stated that he favoured reducing the time limit for terminations to 20 weeks. Today a Roman Catholic archbishop endorsed Mr Howard's stance.

The prime minister will give a lunchtime address next Tuesday to the London-based charitable group, which is largely comprised of evangelical Christians.

No details have been made available of Mr Blair's text, though he said at the weekend he too had personal difficulties with abortion.

In so doing he followed in the footsteps of the Liberal Democrat leader, Charles Kennedy, who was brought up a Roman Catholic, and Michael Howard, who is Jewish.

Traditionally, religious groupings have not exerted a lobbying influence en masse in British politics; however, the Lords today debates a bill that would see a new offence of "incitement to religious hatred" - a move largely welcomed by faith groups but opposed by some artists and atheist groups.

Both Labour and the Liberal Democrats are engaged in a fierce battle to win Muslim votes in the wake of the Iraq war, while in the capital Labour fears London's mayor, Ken Livingstone, may have alienated part of the Jewish vote with his attack on an Evening Standard reporter who later revealed himself to be Jewish.

But the most significant diversion into US-style, faith-based politics came at the weekend, with an Observer leak of a survey for the magazine Cosmpolitan in which Mr Howard revealed he was in favour of reducing the current 22-week limit for abortions to 20 weeks.

Abortion is an "issue of conscience" within Westminster, where MPs are free to vote according to their personal beliefs rather than by party whip.

However, the issue is traditionally kept on the sidelines during the highly charged atmosphere of an election campaign.

At his party's spring conference in Brighton on Saturday Mr Howard also made reference for the first time to allegedly anti-semitic Labour posters that depicted him as flying pig and as a Shylock- or Fagin- style figure.

He told delegates: "Someone, somewhere must be rattled."

Labour, meanwhile, came under fire earlier this year when the Home Office minister Mike O'Brien wrote a piece for a Muslim newspaper stressing the government's work on behalf of the Muslim community.

The Liberal Democrats have also been targeting disaffected Muslims, with their candidate winning Brent East, in London, from Labour in the immediate aftermath of the war in Iraq.

Meanwhile today the Roman Catholic Archbishop of Westminster, Cardinal Cormac Murphy O'Connor, praised Mr Howard as he issued a letter urging Catholics to question parliamentary candidates on six key policy issues ahead of the next general election.

Though the Catholic Bishops' Conference of England and Wales will not expressly recommend one party to worshippers, it suggests voters closely scrutinise candidates on their attitudes to right-to-life issues and marriage. "It is very important that this debate has been opened into the public arena, both in the lead-up to and after the election," said Cardinal O'Connor.

"Abortion, for Catholics, is a very key issue, we are totally opposed to it. The policy supported by Mr Howard is one that we would also commend, on the way to a full abandonment of abortion."

Catholics have also been advised to look specifically at party policies on education, criminal justice, refugees and migrants and the global common good.

Mr O'Connor admitted that may mean a break with traditional backing for the Labour Party.

"I think, as bishops, we are not going to suggest people support one particular party," he said.

"There has been a notion in the past that Catholics would be more in support of the Labour party because they were working class people.

"Now I'm not so sure that will be quite so true today. The Labour party has developed."